My Nana has bugs flying around her tree. It looks like a short skinny wasp, black and white
with orange legs and white feet. It flies with its back legs pointing back. What are they?

John Charles, an entomologist at HortResearch's Mt Albert Research Centre, responded.

What a marvellous description! You have been very observant, and your notes are
much better than those of most adults who ask me to identify insects.

Your insect is almost certainly a parasitoid wasp called Glabridorsum stokesii.
There are millions of different insects in the world, and about 20,000 species in
New Zealand. This means that there are far too many for them to have a
‘common name’ (like ‘orange legged wasp’), so scientists give each one a
two-word name in latin. This is the language that many scientists used 200 years
ago when the naming system was introduced; but it does mean that many insect
names are difficult to pronounce!

Glabridorsum stokesii is a good-guy, because it attacks and kills some of the caterpillars
that eat our fruit trees. The wasp you saw was probably looking for prey on your
Nana’s tree. When it finds one, it injects an egg inside the caterpillar. The egg
hatches into a small grub which eats all of the insides of the caterpillar while it is
still alive. This is pretty gross, but a very effective life-style – all you can eat,
and protected from rain and enemies. Eventually the wasp does kill the caterpillar,
and the adult wasp eats its way out into the open and flies away to look for another one.

Wasps with this biology are called parasitoids, and are unique to the insect world.
There are hundreds of thousands of species, and they are very important.
Without them our world would be overrun with insect pests.